The present invention relates to a dynamic damping control mechanism for wire rope used in operation of heavy earth-moving machine, such as draglines, and the like, as frequently used in mining operations and construction.
Wire rope is a fundamental component in heavy earth-moving equipment such as draglines and electric mining shovels. Wire rope is the mechanism by which a bucket is positioned for dragging and hoisting the payload in the dragline application, and hoisting and/or crowding in the shovel application. Wire rope can also be a mechanism by which engaged structures are supported (e.g. the boom or mast of a dragline or shovel). As such, optimizing wire rope life is of paramount importance to ensure equipment availability and reduce operational costs.
During operation of heavy earth-moving equipment such as a dragline, particularly in digging, wire ropes are subjected to stresses and shock loading that induce standing wave vibration in the wire rope. Left uncontrolled, the wire ropes undergo extreme excursions. The wire rope used on large surface mining equipment is often large diameter steel wire rope, up to 5.00″ in diameter in some cases. This large diameter wire rope is very heavy, and oscillations and movement (or whipping) thereof without damping can cause substantial damage to the rope, the supporting rope sheaves and the supporting structures due to the high inertial loads of the whipping rope.
In a positional mode (e.g. during digging, lifting, and lowering of the bucket), drag rope (in the form of wire rope) exiting the fairlead at the swivel frame assemblies follows the position of the wire rope which are subjected to stresses and shock loading that induce standing wave vibration in the wire rope. Extreme excursions in the positional mode translate into interference with the wrapping of the wire rope on the drum or an intermediate sheave assembly and necessarily require large clearances around the rope path to avoid contact with surrounding structure and equipment.
In a suspension support mode, pronounced excursions are present in dragline equipment where the amount of unsupported length of wire rope is extensive and the unit weight of the wire rope is large. Extreme excursions in the suspension support mode translate to fatigue of the individual wire strands at respective points of connection. The excursions are especially pronounced in dragline equipment where the amount of unsupported length of wire rope is extensive and the unit weight of the wire rope is large.
Both conditions (fatigue of the wire strands and interference with wrapping on the drum and/or sheave) necessarily limit the manner in which the dragline equipment is designed and operated. In both wire rope modes (positional control and suspension support), it is highly desirable to dampen the oscillations in the rope. However, too much rope-movement damping or too little damping may result in similar detrimental effects.
Prior attempts to dampen the pivoting action of the two swivel sheave frames through which the wire ropes pass have included mounting a connecting member between the two swivel frames. A number of different connecting members have been utilized, including a fixed orifice hydraulic damper, a solid metal bar, large rubber donuts, and a large mining truck tire mounted between the two frames.
The conventional dampers being utilized have fixed damping characteristics and do not allow for adjustment of the dampening characteristics which can vary heavily due to changing loading conditions, operator input, environmental factors, and digging conditions, etc. Currently to change the damper characteristics to a different fixed damping force, the dampers need to be removed, disassembled, machined, reassembled, and reinstalled. This is not a very cost effective or timely solution. Further, conventional friction-type dampers rely on abrasion, which leads to wearing of materials which leads to inconsistent and variable damping characteristics over the life of the damper, as well as a constant degradation of the components. The wearing of these dampers requires maintenance on a continual basis. This maintenance is often neglected and the performance of the dampers suffers greatly. Likewise, the friction-type dampers do not provide as desirable of a dampening effect as a viscous fluid damper.